(NEHA) Call Girls Pushkar Booking Open 8617697112 Pushkar Escorts
Uobj paper 2014_123128435
1. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨٠٣
Effect of Quenching Media, Heat Treatment and
Alloying Elements on Properties of Al-Si-Mg Alloy
Abdulazeez O. Mousa Al-Uqaily Jassim M.Salman Al-Murshdy
College of Sci.-Babylon University College of Materials Eng. -Babylon University
azizliquid-2005@yahoo.com jmsmaterials@yahoo.com
Abdalla H. Mihdy Jassim
College of Computer Sci. & Mathematics- Al-Qadisiya University
abd-has85@yahoo.com
Abstract
Al-Si-Mg alloys have been widely used in automotive and aircraft industries for their good
properties, high strength-to-weight ratio and good corrosion resistance. This study aims to preparing of Al-
Si-Mg alloy and study the effect of quenching media (polymer solution and water) ,heat treatment and
effect of addition alloying elements (B & Ti) on the properties of prepared Al-Si-Mg alloy such as
microhardnes and studying the thermal age hardening behavior with artificial ageing time (2-10) hours at
temperatures (150,175,200) .The results showed that the addition of 0.15% B with 1% Ti together to base
alloy improve Vickers microhardness by (57%) at homogenization condition compared with the base alloy,
also the results showed that improvement in thermal stability at ageing temperature 175 when quenching in
polymer solution in comparison with the quenching in water. Mechanical properties of prepared alloys
were measured by using ultrasonic wave technique, also the microstructure of prepared alloys were
appeared by using optical microscopic.
Keywords: Al-Si-Mg Alloy, Mechanical Properties, Quenching, Heat Treatment, Ageing
ﺍﻟﺨﻼﺼﺔ
ﺴﺒﺎﺌﻙ)ﺃﻟﻤﻨﻴﻭﻡ-ﺴﻴﻠﻜﻭﻥ-ﻤﻐﻨﻴﺴﻴﻭﻡ(، ﺠﻴﺩﺓ ﺨﻭﺍﺹ ﻻﻤﺘﻼﻜﻬﺎ ﻭﺍﻟﺴﻴﺎﺭﺍﺕ ﺍﻟﻁﺎﺌﺭﺍﺕ ﺼﻨﺎﻋﺔ ﻓﻲ ﻭﺍﺴﻌﺔ ﺒﺼﻭﺭﺓ ﺘﺴﺘﺨﺩﻡ
ﺠﻴﺩﺓ ﺘﺂﻜل ﻭﻤﻘﺎﻭﻤﺔ ﻭﺯﻨﻬﺎ ﺇﻟﻰ ﻨﺴﺒﺔ ﻋﺎﻟﻴﺔ ﻭﻤﺘﺎﻨﺔ.ﺍﻟﺴﺒﻴﻜﺔ ﺘﺤﻀﻴﺭ ﺍﻟﻰ ﺍﻟﺒﺤﺙ ﻴﻬﺩﻑAl-Si-Mgﺍﻻﺨﻤﺎﺩ ﻭﺴﻁ ﺘﺎﺜﻴﺭ ﻭﺩﺭﺍﺴﺔ)ﻤﺤﻠﻭل
ﻭﺍﻟﻤﺎﺀ ﺍﻟﺒﻭﻟﻴﻤﺭ(ﻭﺍﻟﻤﻌﺎﻤﺍﻟﺴﺒﻙ ﻋﻨﺎﺼﺭ ﺇﻀﺎﻓﺔ ﺘﺄﺜﻴﺭ ﻭ ﺍﻟﺤﺭﺍﺭﻴﺔ ﻠﺔ)ﻭﺍﻟﺘﻴﺘﺎﻨﻴﻭﻡ ﺍﻟﺒﻭﺭﻭﻥ(ﺍﻟﺼﻼﺩﺓ ﻤﺜل ﺍﻟﻤﺤﻀﺭﺓ ﺍﻟﺴﺒﻴﻜﺔ ﺨﺼﺎﺌﺹ ﻋﻠﻰ
ﺍﻻﺼﻁﻨﺎﻋﻲ ﺍﻟﺘﻌﺘﻴﻕ ﺯﻤﻥ ﻤﻊ ﺍﻟﺤﺭﺍﺭﻱ ﺍﻻﺼﻼﺩ ﺴﻠﻭﻙ ﻭﺩﺭﺍﺴﺔ ﺍﻟﺩﻗﻴﻘﺔ))١٠-٢ﺍﻟﺤﺭﺍﺭﺓ ﺩﺭﺠﺎﺕ ﻋﻨﺩ ﺴﺎﻋﺔ)١٥٠،١٧٥،٢٠٠.(ﺒﻴﻨﺕ
ﺃﻀﺎﻓﺔ ﺍﻥ ﺍﻟﻨﺘﺎﺌﺞ٠,١٥%Bﻤﻊ١%Tiﻟﻠﺴﺒﻴ ﹰﺎﻤﻌﺒﻨﺴﺒﺔ ﻓﻜﺭﺯ ﺼﻼﺩﺓ ﺘﺤﺴﻥ ﺇﻟﻰ ﺃﺩﻯ ﺍﻷﺴﺎﺱ ﻜﺔ)٥٧(%ﺍﻟﻤﺠﺎﻨﺴﺔ ﻅﺭﻑ ﻋﻨﺩ
ﺍﻷﺴﺎﺱ ﺍﻟﺴﺒﻴﻜﺔ ﻤﻊ ﺒﺎﻟﻤﻘﺎﺭﻨﺔ.ﺘﻌﺘﻴﻕ ﺤﺭﺍﺭﺓ ﺩﺭﺠﺔ ﻋﻨﺩ ﺍﻟﺤﺭﺍﺭﻴﺔ ﺍﻻﺴﺘﻘﺭﺍﺭﻴﺔ ﻓﻲ ﺘﺤﺴﻥ ﺃﻅﻬﺭﺕ ﺍﻟﻨﺘﺎﺌﺞ ﻭﻜﺫﻟﻙ١٧٥ﻓﻲ ﺍﻹﺨﻤﺎﺩ ﻋﻨﺩ
ﺍﻟﻤﺎﺀ ﻓﻲ ﺍﻹﺨﻤﺎﺩ ﻤﻊ ﻤﻘﺎﺭﻨﺔ ﺍﻟﺒﻭﻟﻴﻤﺭ ﻤﺤﻠﻭل.ﻟﻠﺴﺒﺎ ﺍﻟﻤﻴﻜﺎﻨﻴﻜﻴﺔ ﺍﻟﺨﺼﺎﺌﺹ ﻗﻴﺎﺱ ﺘﻡﺍﻟﺼﻭﺘﻴﺔ ﻓﻭﻕ ﺍﻟﻤﻭﺠﺎﺕ ﺘﻘﻨﻴﺔ ﺒﺎﺴﺘﺨﺩﺍﻡ ﺍﻟﻤﺤﻀﺭﺓ ﺌﻙ
ﺍﻟﻀﻭﺌﻲ ﺍﻟﻤﺠﻬﺭ ﺒﺎﺴﺘﺨﺩﺍﻡ ﺍﻟﻤﺤﻀﺭﺓ ﻟﻠﺴﺒﺎﺌﻙ ﺍﻟﻤﺠﻬﺭﻴﺔ ﺍﻟﺒﻨﻴﺔ ﺇﻅﻬﺎﺭ ﺘﻡ ﻭﻜﺫﻟﻙ.
ﺍﻟﻤﻔﺘﺎﺤﻴﺔ ﺍﻟﻜﻠﻤﺎﺕ:AL-ﺳﻲاﻟﻤﻐﻨﯿﺴﯿﻮم،أﻟﻤﻨﯿﻮماﻟﻤﯿﻜﺎﻧﯿﻜﯿﺔ اﻟﺨﻮاص،ﺗﺴﻘﯿﮫ،اﻟﺤﺮارﯾﺔ اﻟﻤﻌﺎﻟﺠﺔ،ﺷﯿﺨﻮﺧﺔ
Introduction
For over fifty years, aluminum ranks at second to iron and steel in the metal
market. The demand of aluminum grows rapidly because it is attributed to unique
combination of properties which makes it become one of the most versatile of
engineering and construction materials (Masoud,2012).Aluminum alloys have many
desirable properties such as high fluidity, light weight, low melting points, high thermal
conductivity and good surface finish these properties making aluminum alloys for using
widely in casting, Aluminum alloys with silicon as a major alloying element constitute a
class of material, which provides the most significant part of all shaped castings
manufactured especially in the aerospace and automotive industries(Al-Khazraji,2011).
In recent decades, aluminum alloys used in the automobile industry as car body panels to
reduce weight and thus improve fuel economy and emissions) Abozeid and
(Gaber,2012)..Addition of alloying elements such as magnesium and silicon to aluminum
improve mechanical properties of aluminum and increase the aluminum response to heat
2. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨٠٤
treatment due to formation of Mg٢Si intermetallic compound, which improves the
casting, corrosion resistance property as well as the strength of the alloy(Oladele and
Omotoyinbo,2011). Al−Si−Mg alloys are widely used as medium-strength heat-treatable
alloys for structural applications due to their excellent formability, weldability and good
corrosion resistance. In Al −Si−Mg alloys, Mg and Si are added either in a balanced
amount to form binary Al−Mg٢Si alloys or with excess amount of Si to form the
Al−Mg٢Si quasi-binary composition, to enhance the kinetics of the precipitation process
without changing the nature of precipitates (Li,2013). The heat treatment is one of the
important methods for improving the mechanical properties of Al-Si-Mg alloys this heat
treatment consists of solution heat treatment , quenching, and then either natural or
artificial ageing (Moldovan,2007). Quenching is one of the crucial heat treatment
processes for manufacture of the products with desired mechanical properties
(Kakhki,2011). The quenching is the process of rapid cooling of materials to room
temperature to preserve the solute in solution. The cooling rate needs to be fast enough to
prevent solid – state diffusion and precipitation of the phase. The rapid quenching creates
a saturated solution and allows for increased hardness and improved mechanical
properties of the material (Abubakre,2009). Quenching may be performed by means such
as total immersion in an aqueous polymer solution, liquefied gas, cold water, hot water,
or boiling water, or by air blast or fog( ASTM Designation,2001). Also quenching is
performed in oil (Deval,2013). Cold water used to be the dominant quenchant for heat
treating aluminum alloys. However, in many cases, cold water quench produces
unacceptable distortion due to high thermal gradients induced upon cooling( Shuhui,
2006). Aqueous solutions of polyalkylene glycol (PAG) are used to improve the cooling
characteristics of the quenching medium and to reduce the machining requirements after
the heat treatment. PAG concentrations vary from (4 to 30)%, depending on the type of
product being processed. For the heat treatment of aluminum alloys, such polymeric
solutions have been widely applied during more than 30 years (Al-Sultani,2012).
Ultrasonic waves are propagated through the material and the waves are disrupted at the
discontinuities in the material such as defects, voids, or cracks. The waves are scattered
or partially reflected at these discontinuities and from this action, a measure of the
discontinuity characteristics such as location, size, and shape are revealed. The ultrasonic
method does not always reveal everything about the discontinuity to the degree desired
but is still an invaluable tool (Kutz,2002 .(The aim of the present study was to studying
the effect of quenching media) water and 35% PAG (and alloying elements boron (B)
and titanium (Ti) on properties of prepared Al-Si-Mg alloy .
Experimental Work
Aluminum wires were cut into small pieces and melting in an electric furnace at
temperature 750 after putting in Alumina crucibles, then addition of alloying elements in
the required weight percentages where remain for (5-10) minutes after each element
addition. During addition of alloying elements must be continuous mixing by using a
graphite stirring rode to ensure a best mixing and dissolution of alloying elements and to
avoid segregation defects. All alloying element are packing with Al-foils to avoidance of
oxidization. Finally, the molten alloy is pouring in the steel mold and after solidification,
the steel mold is opening to obtain the ingot rods. The above steps were repeated for the
various aluminum alloys which used in this work. The chemical composition of prepared
alloys as shown in Table (1). Alloy specimens were prepared and subjected to three
3. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨٠٥
different heat treatment conditions .The first treatment was subjected the specimens to
homogenization treatment at temperature (430) for three hours ,the second treatment was
subjected the specimens to solid solution treatment at three temperatures (500,525,550)
for one hours in order to select one among these degrees which obtained good
microhardness, then quenching rapidly in two different quenchant media (water and 35%
PAG polymer type polyethylene glycol), and the finally treatment was subjected the
specimens to artificial ageing at temperature (150,175,200) at different times.
Table (1) The chemical composition of prepared alloys.
Tests and Measurements
Microhardness test
Microhardness test was measured of the specimens by using Vickers tester type
(Microhardness tester Hv-1000) . For achieving of the hardness test was used load 100g
for 10s. Microhardness of the specimens was measured after of the homogenization,
solution treatment, and ageing. This test was carried out in the (Laboratory of
Metallurgical /College of Materials Engineering /Babylon University).
Ultrasonic Wave Test
Ultrasonic wave technique was used to determined the mechanical properties of
alloys by finding the speed of ultrasonic wave in the specimens by measuring time delay
of ultrasonic wave in the specimen and thickness of this specimen by using equipment of
measuring ultrasonic wave type (SVX-7 made in Korea). This test was carried out in the
(Laboratory of Advanced Polymer/ Department of Physics/College of Science /Babylon
University). The acoustic velocity (υ) in the material is the acoustic path length which is
determined by timing the passage of ultrasound. The velocity of the ultrasound in a
material depends on elastic constants and density of that material .The ultrasonic velocity
in the sample is obtained by dividing the measured value of the acoustic path length (l) by
the time of travel (t). The acoustic impedance (Z) is equal to the product of the density
(and velocity (υ) of the sound of the material, the value of the acoustic impedance
depends on its physical properties. Modulus of elasticity (E) is equal to the product of the
density (and square of velocity of sound of the sample (Lochab and Singh,2004).The
compressibility (C) is the reciprocal of the modulus of elasticity (Al-bermany,2013).
υ=l/t …...…………..…………....(1)
Z=υ …….…...…….....................(2)
E=υ 2
...........................................(3)
4. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨٠٦
C =(υ 2
)-1
..… …..….…………...(4)
The density of alloys can be calculated according to the equation:
l
d
W
V
M
p
4
2
………………….…(5)
Where, ),,,( landdVMp is the density ,mass , volume , diameter, and thickness of the
samples respectively.
X-Ray Diffraction Test
The aim of doing the X-ray diffraction analysis was to identify the type of Al-
alloy phases formed during casting and for measured grain size .
This test was performed through scanning the specimen continuously within
Bragg angle (2θ) range (30º-70º) using Cu target (λ=0.154 nm) at voltage of 40 kV and
30 mA of current with continuous scan mode by general electric diffraction type(XRD-
6000).
X-ray diffraction test was carried out in the (Ministry of Sciences and
Technology/ Research Office of Materials).
Optical Microscopic Testing
Optical microscopy was used to provide information about the microstructure of
alloy samples. Microstructure of alloys were appeared after each heat treatment with
magnification (400X) by using ( SIMRAN optical microscope made in USA).Before
doing this test, the specimen surface was etched to Keller’s reagen solution which
consists of 95% O, 2.5% , 1.5% HCl and 1%HF.This test was carried out in the
(Laboratory of Metallurgical /College of Materials Engineering /Babylon University).
Results and Discussion
Microhardness Results at Homogenization
The microhardness measurement for alloys (A, B ,C ,and D) after process of
homogenized for three hours at 430 and slow cooled to room temperature as follows
shown in Table (2).
Table (2) Microhardness of the alloys as homogenized
Table (2) shows the microhardness of alloys (A, B ,C ,and D).The microhardness
increased with the alloys (B, C,D) because the alloying elements (B and Ti) accelerated
and refined the precipitates which form previously in base alloy (A alloy) such as (Mg2Si
and Al3Mg2) and production a new precipitates such as AlB2,Al3Ti,TiB, and TiB2.From
Table (2), (D alloy) appears increase in hardness by (57%) corresponding to the base
alloy because it contains elements such as (B and Ti) and these elements work to produce
fine grains.
5. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨٠٧
Microhardness Results at Solid Solution Treatment
The microhardness measured for alloys(A, B,C, and D) after solid solution
treated for one hour at three solid solution temperatures (500, 525 and 550) for
choosing the best solid solution temperature which corresponding to the maximum
microhardness and used two different quench mediums ,firstly distil water and secondly
35% PAG. The relationship between Vickers microhardness and solid solution
temperatures for two different quench mediums appears in Figure(1). From this figure it
could be concluded that the better solid solution temperature was 525, since it gives high
solubility for elements within solid solution (α-Al). 500 not give full solubility for
elements within solid solution (α-Al). 550 give full solubility for elements with in solid
solution (α-Al) but produce grain growth for (α-Al) (Tan and Ögel,2007), and the average
size of the remand precipitated particles increases with temperature, and the total number
of particles in the system decreases because larger particles tend to grow at the expense of
the smaller ones, which shrink disappear and it is causes the decrease in
microhardness.Furthermore, the difference in quench media affected on microhardness
when water quenching gives higher microhardness values because water faster loses the
temperature in comparison with a polymer solution. Water does not permit elements to
diffuse from solid solution (α-Al) and precipitate on grain boundary.
Fig. (1) Variation of microhardness of (A,B,C,and D) alloys (quenching in a: water
medium, b: 35% PAG medium ) with solid solution temperatures.
Microhardness Results at Ageing Temperature 150
The relationship between Vickers microhardness and exposure time at ageing
temperature 150appears in Figure (2).
6. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨٠٨
From Figure (2) it is notice that increment in microhardness of (A alloy) with
ageing time for both water and polymer quenching and reaches the highest peak at the 8
hours of ageing time then dropped at the10 hours of ageing time. It is concluded that (A
alloy) (quenched in water) have maximum value of microhardness at ageing time 8
hrours which was 99.67 kg/mm2
, and the same alloy quenched in 35% PAG have
maximum value of microhardness at ageing time 8 hours also was 89.01kg/mm2
because
the medium of water was faster in accelerate quenching than PAG. Therefore, grain size
(α-Al) in (A alloy)(quenched in water) become very fine grain. From Figure (2) it can be
seen that microhardness of (B alloy) reaches the highest peak at the 6 hours of ageing
time then dropped at the (8-10) hours of ageing time for both water and polymer
quenching.It was concluded that (B alloy)( quenched in water and 35% PAG) caused an
increase in thermal age hardening behavior by (12% and 14 %) respectively than (A
alloy)(quenching in water and 35% PAG ) because the element of boron in (B alloy)
done really fine grain of matrix and precipitate causes increments in a thermal age
hardening.
From Figure (2) it can be seen that microhardness of (C alloy) slightly increase
with ageing time from (100.39 to 119.92) kg/mm2
for water quench and from
(93.61 to 110) kg/mm2
for polymer quench within the first 6 hours of ageing at a
temperature of 150, then microhardness decreases to 97.51 kg/mm2
for water quench and
90.31 kg/mm2
for polymer quench after 4 hours of ageing as shown in microhardness
curve, and this curve appears the (C alloy) quenched in water have maximum values of
microhardness than when quenched in 35% PAG because the medium of water is
accelerate quenching than PAG. Therefore, grain size (α-Al) in (C alloy)( quenched in
water) became very fine grain, and caused high microhardness. From Figure (2) it is
concluded that (C alloy)( quenched in water and 35% PAG) caused an increase in
microhardness value by (23%,25%) respectively than (A alloy)(quenching in water and
35% PAG ) because the elements of titanium in (C alloy) have high thermal stability.
Figure (2) shows slightly increase in microhardness of (D alloy) with ageing
time until reaches maximum peak at 6 hours of ageing time ,then dropped at (8-10) hours
of ageing time for both water and polymer quench. From Figure (2), it is concluded that
(D alloy) ( quenched in water and 35% PAG) caused an increase in thermal age
hardening behavior by (28% and 31 %) respectively than (A alloy)(quenching in water
and 35% PAG ) because the elements of boron and titanium in (D alloy) done really fine
grain of matrix and precipitate causes increments in a thermal age hardening.
7. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨٠٩
Fig.(2) Variation of microhardness of (A,B,C,and D) alloys (quenching in a: water
medium, b: 35% PAG medium ) with ageing time at 150ageing temperature.
Microhardness Results at Ageing Temperature 175
The relationship between Vickers microhardness and exposure time at ageing
temperature (175) appears in Figure (3).From this figure, it is notice that microhardness
of (A alloy) dropped until (87.03, 78.26) Kg/mm2
for water and 35% PAG respectively at
2 hours of ageing time. Extended ageing time notice that microhardness increases and
reaches highest peak value of (105.88 , 96.25) Kg/mm2
for water and 35% PAG
respectively at 6 hours of ageing time, then slightly decreases until reaches to (98.16 ,
89.43) Kg/mm2
for water and 35% PAG respectively at 10 hours of ageing time. It is
concluded that thermal age hardening behavior at 175ageing temperature is the best in
comparison with the same alloy which aged at ageing temperature 150[Figure (2)]
because the microhardness curve at ageing temperature 175after highest peak it is
appeared approximately more linear than this curve at ageing temperature 150 . That is
means the little change in microhardness with ageing time at temperature 175 indicate to
the best thermal age hardening behavior at this temperature especially when quench in
polymer.
8. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨١٠
Fig.(3) Variation of microhardness of (A,B,C,and D) alloys (quenching in a: water
medium, b: 35% PAG medium ) with ageing time at 175ageing temperature.
Figure (3) shows that the highest peak of microhardness of (B alloy) at 4 hours
of ageing time then microhardness decreases slightly at (6-10) hours of ageing time for
both water and 35% PAG.It is concluded that (B alloy) (quenched in water and 35%
PAG) caused an increase in thermal age hardening behavior by (17% and 19%)
respectively than (A alloy)(quenching in water and 35% PAG ) because the elements of
boron in (B alloy) done really fine grain.
From Figure (3) it is notice that microhardness of (C-alloy) increases slightly
with increase of ageing time and reaches to highest peak at 4 hours of ageing time and it
is concluded that (C alloy)( quenched in water and 35% PAG) caused an increase in
thermal age hardening behavior by (21% and 23 %) respectively than (A
alloy)(quenching in water and 35% PAG ) because the elements of titanium in (C alloy)
have high thermal stability.
Figure (3) shows that microhardness of (D alloy) increased slightly with
increasing of ageing time until reaches to the highest peak at 4 hours then decreased
slightly at (6-10)hours for both water and 35%PAG quenched, and it is concluded that
(D alloy) (quenched in water and 35% PAG) caused an increase in thermal age hardening
behavior by (32% and 35% ) respectively than (A alloy)(quenching in water and 35%
PAG ) because the elements of boron and titanium ( in D alloy) done really fine grain.
By comparison with Figure (2) it is concluded that thermal age hardening behavior of (D
9. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨١١
alloy) at 175 ageing temperature is the best than the same alloy which aged at ageing
temperature 150 because the microhardness values at 175appeared lowest varies with
ageing time than values at 150
Microhardness Results at Ageing Temperature 200
The relationship between Vickers microhardness and exposure time at ageing
temperature (200) appears in Figure (4).This figure presents the variation of
microhardness as function of the ageing time at 200. It can be seen the highest peak of
microhardness of (A alloy) at 4 hours of ageing time for both water and 35%PAG
quenched then decreases gradually with an increase of the ageing time from (6-10) hours
because the ageing process had reached the over aged region and the precipitate particles
continued coalesce as ageing progress caused the particle size to increase and thus
decreased the degree of complication for the dislocations to break the magnesium-silicon
bonds when they pass through the precipitates.
From Figure (4) it can be seen the maximum microhardness of (B alloy) at the 2
hours of ageing time for both water and 35%PAG quenched then decreases gradually
with an increase of the ageing time at the (4-10) hours and reduces the ageing time
required to reach microhardness the highest peak. It is concluded that (B alloy)
(quenched in water and 35% PAG) caused an increase in thermal age hardening behavior
by (10% and 15 %) respectively than (A alloy)(quenching in water and 35% PAG ) for it
is contains the elements of boron.
Fig.(4) Variation of microhardness of (A,B,C,and D) alloys (quenching in a: water
medium, b: 35% PAG medium ) with ageing time at 200ageing temperature.
Figure (4) shows that the highest peak of microhardness of (C alloy) at the 2
hours of ageing time then decreases gradually with an increase of the ageing time at
the(4-10) hours and it can be seen that reducing the ageing time at 200required to reach
the highest peak in comparison with the same alloy (C alloy) at (150 and 175). By
comparison with (A alloy) it is concluded that (C alloy)( quenched in water and 35%
10. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨١٢
PAG) caused an increase in thermal age hardening behavior by (20% and 24 %)
respectively than (A alloy)(quenching in water and 35% PAG ) for it is contains the
elements of titanium.
Figure (4) shows that the highest peak of micohardness of (D alloy) at the 2
hours of ageing time for both water and 35%PAG, then decreases gradually with an
increase of the ageing time at the (4-10) hours and it can be seen that reducing the ageing
time at 200 required to reach the highest peak in comparison with the same alloy (D
alloy) at (150 and 175) . By comparison with (A alloy) it is concluded that (D alloy)
(quenched in water and 35% PAG) caused an increase in thermal age hardening behavior
by (27% and 32%) respectively than (A alloy)(quenching in water and 35% PAG) for it is
contains the elements of boron and titanium.
From all ageing temperature it can be seen that the increasing ageing
temperature yielded to reduced the ageing time which required to reach the highest peak
of microhardness.
Ultrasonic Results
The velocity of sound in a material depends on the elastic constant and density of
those material. Thus, direct measurements of velocity determine the elastic constant
provided that the density can be evaluated by another method, example by measuring
volume and weighing. Both the elastic constant and the density vary with the
temperature, concentration, structure and nature of alloy. The measurement of velocity
may yield information about one of these quantities provided that the others remain
constant or can be measured independently. Ultrasonic velocity in alloys was measured
by dividing the path length (thickness of the sample) by the delay time [equation
(1)].Acoustic impedance, elastic modulus, and compressibility were measured by using
equations[(2),(3), and (4)] respectively. Table(3) shows the ultrasonic results for prepared
alloys at homogenization state . From Table(3) it can be seen the highest value of
ultrasonic speed in (D alloy) which contains the elements of (B and Ti) and ultrasonic
speed in (C alloy) contains the element of (Ti) is higher than in (B alloy) contains the
element of (B), these variation in ultrasonic in alloys resulted from the effective of the
microhardness and density of alloys, where the ultrasonic speed increased with the
increase of the microhardness and density of the medium and the highest microhardness
resulted from the uniformly homogeneity of the distribution and diffusion of the alloying
elements in the aluminum matrix so that ultrasonic wave propagated and traveled with
faster in alloy that have highest microhardness. The variations in acoustic impedance,
elastic modulus, and compressibility of prepared alloys are resulted from the variations
in ultrasonic speed and density of these alloys. The density of prepared alloys were
calculated by using the equation (5).
11. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨١٣
Table(3) Ultrasonic results of prepared alloys.
X-Ray Diffraction Analysis
The aim of doing the X-ray diffraction analysis was to determine the crystal
structure and the phases appearance in prepared alloys .In this test ,type of the crystal
structure was determined by using computer programmer "International Center for
Diffraction Data (ICDD 1997)", and it is found that (A alloy) consists of Cubic and
Tetragonal structure. B alloy consists of Cubic, Hexagonal ,and Tetragonal structure .
Figures(5) and (6) show X-ray diffraction patterns of (A and B alloys), which shows a set
of phases that are developed during the ageing process of the alloys. These phases are
mainly consist of (Al2Mg) and (AlB2) phases for (D alloy) which around the major phase
α-Al, while (A alloy) consists of (Al2Mg) phase in which around the major phase α-Al.
Fig. (5) XRD Pattern of (A alloy) at the as-aged state.
Fig. (5) XRD Pattern of (B alloy) at the as-aged state.
12. Journal of Babylon University/Engineering Sciences/ No.(4)/ Vol.(22): 2014
٨١٤
Optical Microscopic Results
The microstructure of alloys as homogenization that used in this study is shown
in Figure (6), and it is noted that most of the grains in this condition which appear much
equiaxed structure and observed precipitates present on the grain boundaries to alloys.
Figure (7) shows microstructure of alloys when quenching in two different media ( water
and 35% PAG) from solid solution temperature and this figure shows that the alloys
quenched in water have been high supersaturated solid solution this because of the high
cooling rate, the alloy which quenched in polymer allows for it to go out small amount of
solute atoms to precipitate on grain boundary due to lower cooling rate.
Fig. (6) Microstructure of (A, B,C and D) alloys as homogenization treatment, X 400
Fig.(7) Microstructure of (A, B,C and D) alloys as solution heat treatment (quenching in
a: water medium, b: 35% PAG medium ), X 400
Conclusions
The conclusions of this work can be summarized as follows:
The better solid solution temperature was 525 which gives high solubility for
elements within solid solution(α-Al).
The addition of 0.15% B with 1% Ti together to the base alloy improves Vickers
microhardness by (57%) at homogenization state compared with the base alloy.
The addition of 0.15% B with 1% Ti together to the base alloy improves thermal age
hardening behavior by (32%) when quenched in water, and by (35%) when quenched
in 35%PAG at 175 in comparison with the base alloy.
Addition of boron and titanium together to the base alloy makes ultrasonic wave
travels faster.
